Thermal diffusivity measurements

Thermal diffusivity measurements of polymers were made for the first time by... 

Ueberreiter and collaborators (12, 13, 14) but have remained relatively unknown. In their earlier work the authors tried to calculate the heat conductivity X from these thermal diffusivity measurements by means of the relation... 

R. Righini and A. Cezairliyan, Pulse Method of Thermal Diffusivity Measurements, A Review , High Temperatures-High Pressures, 5 481-501 (1973). 

Thermal diffusivity measurements were performed on pellets by the use of a transient response technique. Pellets of cellulose or char were instrumented with thermocouples at known distances from the surface. Samples were then brought into contact with a hotplate whose surface temperature varied in an approximately sinusoidal manner. Samples of virgin cellulose could only be tested up to surface temperatures of about 500 K, to avoid pyrolysis. Char samples could be tested to temperatures up to those seen during pyrolysis (in excess of 750 K). Samples were covered by a bell jar, purged with nitrogen, in order to avoid reactions with oxygen. 

Heat capacities were determined by using a differential scanning calorimeter (DSC). A sapphire standard was used for DSC cell calibration. Samples were cut directly from the samples used in the thermal diffusivity measurements. Heat capacity was determined, as usual, from the heat requirement of the sample in response to a particular change in temperature. Multiple scans were performed to verify that sample degradation did not influence the results. Char samples could be heated up to 850 K in these experiments. The DSC cell was continuously purged with nitrogen, in order to avoid oxidation of the samples. 

Thermal diffusivity measurement for SiC/C compositionally graded graphite materials... 

Another method for measuring thermal diffusivity is the flash method developed by Parker et al. [48] and successfully used for the thermal diffusivity measurement of solid materials [49]. A high intensity short duration heat pulse is absorbed in the front surface of a thermally insulated sample of a few millimeters thick. The sample is coated with absorbing black paint if the sample is transparent to the heat pulse. The resulting temperature of the rear surface is measured by a thermocouple or infrared detector, as a function of time and is recorded either by an oscilloscope or a computer having a data acquisition system. The thermal diffusivity is calculated from this time-temperature curve and the thickness of the sample. This method is commercialized now, and there are ready made apparatus with sample holders for fluids. There is only one publication on nanofluids with this method. Shaikh et al. [50] measured thermal conductivity of carbon nanoparticle doped PAO oil. 

Erensdorff H.K. 1974. Thermal diffusivity measurements on elastomers. Rubber Chem. Technol. 47 849-57. 

Thermal Diffusivity - The thermal diffusivity [D = k/(pCp)] of S10C-N312 BN 2-D composites was determined by the laser flash method in which a laser is used as a heat source and the thermal pulse transmission speed is measured in the desired orientation. Thermal diffusivity measurements were made both in-plane and through-plane ofthe 2-D composite. The specimen size was 9x9x2 mm square. The thermal diffusivity was calculated from solution of the diffusion equation for heat flow with the known boundary conditions. Details of this procedure are found in ASTM Standard Test Method E37.05 (Thermal Diffusivity by the Flash Method). 

THERMAL DIFFUSIVITY. MEASUREMENT TECHNIQUES AND DATA ANALYSIS. QUARTERLY PROGRESS REPT. NO. 11, OCT - DEC 64. 

THERMAL DIFFUSIVITY MEASUREMENTS WITH STATIONARY WAVES METHOD. FROM PROCEEDINGS OF THE SEVENTH CONFERENCE ON THERMAL CONDUCTIVITY. GAITHERSBURG,... 

THERMAL DIFFUSIVITY MEASUREMENTS FROM A STEP FUNCTION... 

DETECTION OF TRANSITION POINTS OF POLYMERS BY COMPARATIVE THERMAL DIFFUSIVITY MEASUREMENTS. 

THERMAL DIFFUSIVITY MEASUREMENTS FROM A STEP FUNCTION CHANGE IN FLUX INTO A DOUBLE LAYER INFINITE SLAB. HALTEMANEK GERRISHRWJR INTERN J HEAT MASS TRANSFER 12 11 1520-4 1969 CA... 

Gustafsson, S.E. (1991) Transient plane source techniques for thermal conductivity and thermal diffusivity measurements of solid materials. Rev. Sci. Instrum., 62, 797-804. 

Heat capacity measurements of Polovov (1973) (300-950 K) are shown only in the form of a small graph, but they detect an anomaly at 694 K which may well correspond to the eutectoid in the samarium-samarium hydride system and they also detect a further anomaly at 830 K which may well be the reduced alpha-beta transformation temperature. Heat capacity measurements of Kurichenko et al. (1985) (900-1350 K) are also shown in the form of a small graph, but in particular, their thermal diffusivity measurements show an anomaly at 980 K which may also be associated with the alpha-beta transformation. 

Thermal diffusivity measurements have been reported for fibre reinforced phenol-formaldehyde resins [31], PA 6,6, PP, PMMA [54] and trifluoroethylene nanocomposites [55]. 

Thermal Diffusivity Measurement by Temperature Wave Analysis (TWA)... 

Generally, thermal diffusivity measurement has many advantages, such as small sample size, short measuring period and wide temperature range. On this account, it is an important method for obtaining thermal conductivity data. There... 

R. G. Horn, ""Refractive indices and order parameters of two liquit crystals, J. Phys., vol. 39, pp. 105-109, 1978 W. Urbach, H Hervet, and F. Rondelez, ""Thermal diffusivity measurement in ne matic and smectic phases by forced Rayleigh light scattering, Mo lec. Cryst. Liq. Cryst., vol. 46. pp. 209-221, 1978. 

The laser flash method is used for thermal diffusivity measurements. In this technique, a laser is used to pulse one side of a test specimen uniformly. The temperature rise of the other side is measured using an infrared detector. This transient is then used to calculate the thermal diffusivity. While the technique is simple in concept, nonidealities such as heat loss from the front and back surfaces complicate the resulting data analysis, so that fairly complex models need to be used to extract the thermal dilfu-sivity. These calculations can be easily performed by the computers used to run the instruments. 

Thermal conductivity, which is an important parameter for thermal assessment of the core behaviour in the safe-storage safety case, is derived from thermal diffusivity measurements which employ a laser heat-pulse technique defined by a British Standard method (BS 7134 Part 4.2, 1990). 

Baba, T. and Ono, A. 2001. Improvement of the laser flash method to reduce uncertainty in thermal diffusivity measurements. Measuring Science Technology 12 2046-2057. 

Salazar, A., Sanchez-Lavega, A., Fernandez, J., 1993. Thermal diffusivity measurements on solids using coUinear mirage detection. J. Appl. Phys. 74 (3), 1539-1547. 

Tsuchiya, B., Huang, J., Konashi, K., Saiki, W., Onoue, T., Yamawaki, M., 2000. Thermal diffusivity measurement of uranium—thorium—zirconium hydride. Journal of Alloys and... 

By combining DDC measurements and thermal diffusivity measurements it may be possible to predict the limiting heating rate for unidirectional heat flow and reaction. DDC will provide dqjdt as a function of heating rate and reaction rate from surface temperature and thermal diffusivity the temperature profile, dTjdx, may be computed at any time after the reaction temperature is reached at any point, the change in local temperature and flux velocity may be determined. 

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